The disease caused by Mal de Río Cuarto Virus (MRCV) is a major corn disease in Argentina, accounting for yield losses of greater than 70% in years of severe outbreak (Rodriguez P E et al. (1998) Plant Dis. 82:149-52). The disease is a member of Serogroup 2 of Fijivirus, which includes other viruses such as maize rough dwarf virus, rice black streaked dwarf virus, and pangola stunt virus (Uyeda I & Milne R G (1995) Semin. Virol. 6:85-88). The main vector for MRCV is Delphacodes kuscheli, but other Delphacodes species, such as D. haywardi and D. tigrinus, and Toya propinqua have been shown to carry the virus. The virus does not appear to be transmitted to progeny via seeds. Distéfano et al., Arch. Virol. 147:1699-1709 (2002), analyzed the MRCV sequence and proposed that it is a new Fijivirus species related to MRDV (Maize Rough Dwarf Virus). MRDV is found in several European countries (e.g., the Czech Republic, France, Italy, Norway, Spain, Sweden) and in China, while MRCV has been also detected in Uruguay (Ornaghi J. A., Beviacqua J. E., Aguirrezabala D. A., March G. J. and Lenardón S. L. 1999. Detection of Mal de Río Cuarto virus in Uruguay. Fitopatologia Brasileira 24: 471).
MRCV infection causes abnormal maize development and significantly reduces crop yields. The susceptible phenotype includes stunting, shortening of internodes, multiple ears with scattered grain, deformed tassel with no anthers, presence of small enations in the back of the leaves, reduced roots, cut and reduced leaves. Plants symptoms depend on phenological stage of the plant, plant genotype, and environment (Lenardón et al., “Virus del Mal de Río Cuarto en maíz”, in Proyecto de Investigaciones en Fitovirologia (Lenardón ed.), 2:10 (1999). Most severe symptoms occur when infected at the coleoptile—first leaf stage.
In the severe MRCV outbreak of 1996-1997, over 300,000 hectares of maize in Argentina were affected, resulting in losses totaling approximately $120 million. Increased populations of Delphacodes kuscheli in 2006 apparently led to a reoccurrence of the viral disease in Argentinean corn plants, which significantly affected the 2007 harvesting. Susceptible genotypes were strongly affected by MRCV at the endemic region (Córdoba Province) and moderately affected at other maize regions.
The development of molecular genetic markers has facilitated mapping and selection of agriculturally important traits in maize. Markers tightly linked to disease resistant genes are an asset in the rapid identification of resistant maize lines on the basis of genotype by the use of marker assisted selection (MAS). Introgressing disease resistance genes into a desired cultivar would also be facilitated by using suitable DNA markers.